Heredity and Evolution

Fossils are preserved remains, impressions, or traces of organisms that lived in the past. By comparing fossils from rock layers of different ages with living organisms, scientists can identify structural similarities, differences, and changes through geological time. This provides evidence for gradual biological change and evolutionary relationships. Option A is correct; the other choices assign fossils unrelated abilities such as controlling weather or changing blood groups.

The governing geological principle is relative dating: when rock layers have not been greatly disturbed, deeper layers were generally deposited earlier than layers above them. A fossil in such a deeper layer is therefore usually considered relatively older than one in a higher layer. This conclusion is comparative, not an exact numerical age. Option A is correct; B, C, and D contradict the meaning of a fossil and the ordering of strata.

Homologous organs have a similar basic structural plan because of common ancestry, although they may perform different functions. The human hand is adapted for grasping and the horse forelimb for support and locomotion. Their corresponding bones, such as the upper arm, forearm and hand-region bones, reveal the shared plan. Therefore option A is correct; the other choices confuse function, appearance or digestion with structural homology.

Analogous organs perform similar functions but arise from different basic structures and evolutionary histories. For example, wings of birds and insects both support flight, yet a bird wing is a modified bony forelimb while an insect wing develops from a different body structure. Similar environmental demands can produce similar functions without close ancestry. Thus option A is correct; the other choices are biologically false or irrelevant.

Analogous organs have a similar function but different structural plans and evolutionary origins. Both bird wings and insect wings enable flight, so their function is comparable. However, a bird wing is a bony forelimb with feathers, whereas an insect wing is an outgrowth associated with the insect body covering and lacks the bird’s limb-bone plan. Therefore option A is correct, not B, C or D.

An inherited trait is influenced by genetic information received from parents and can be transmitted through reproductive cells. Eye colour depends mainly on inherited genes that affect pigment production, although biological traits can involve several factors. A haircut changes the visible length of hair during an individual’s life but does not alter the genes in reproductive cells. Hence option A is correct; the other options confuse nutrition or acquired changes with heredity.

Biological classification groups organisms according to shared characteristics and reveals patterns of similarity and difference. Organisms with more fundamental similarities may share a more recent common ancestor, while major differences can indicate greater evolutionary separation. Classification alone is not the only evidence; fossils, comparative anatomy, embryology and molecular data also strengthen conclusions. Thus option A is correct, while the other choices describe unrelated or impossible effects.

In evolutionary biology, shared structural, developmental or molecular features can indicate common ancestry. When two organisms show more significant similarities, they may have diverged from a relatively recent common ancestor and therefore have a closer evolutionary relationship. However, one superficial feature is not enough; several lines of evidence should be compared. Option A is correct. The other options wrongly deny relationships, equate species, or deny the presence of genes.

External appearance can be misleading because unrelated organisms may face similar environmental demands and evolve similar shapes or functions. These are analogous similarities and do not necessarily indicate close ancestry. For example, wings of birds and insects both support flight but have different structural plans. Evolutionary relationships should therefore be assessed with internal anatomy, fossils, embryology and molecular evidence as well. Option A is correct; the other choices make absolute or false claims.

Darwin used the idea of struggle for existence to explain competition among organisms for limited food, space, shelter, and mates. Individuals in the same population vary, and some variations provide an advantage in a particular environment. Such organisms are more likely to survive and reproduce, passing those useful inherited traits to offspring. Therefore, option A is correct; the other choices incorrectly describe struggle as total death or as unrelated to biology.

Adaptation refers to a heritable feature that improves an organism’s chances of surviving or reproducing in a particular environment. Natural selection acts on existing variation: organisms with advantageous inherited traits tend to leave more offspring, so those traits may become more common in the population over generations. Thus option A correctly states the relationship. Adaptation is not produced instantly, and selection does not destroy every trait.

If green colour provides camouflage, birds may detect green insects less easily. The insects that survive more often have a greater opportunity to reproduce, and the trait may be passed to their offspring if it is inherited. Across many generations, the proportion of green insects can therefore increase in the population. Option A is correct; natural selection is gradual, does not instantly change every insect, and does not cause birds to lose chromosomes.

Natural selection changes the composition of a population across generations, not merely the condition of one individual. A variation that improves survival or reproduction can influence evolution only when it is transmitted to offspring. If the variation is not inherited, it disappears when the individual dies and cannot become more frequent in the population. Therefore option A is correct; digestion and chromosome destruction are unrelated to this requirement.

A plant with one dominant allele and one recessive allele is heterozygous and usually appears tall because the dominant allele masks the recessive one. It can nevertheless pass the recessive allele to a gamete. If an offspring receives one recessive allele from each parent, its genotype is homozygous recessive, so the dwarf phenotype is expressed. Thus option A is correct; receiving no gene is impossible and a dominant allele masks dwarfness.

Evolution is a change in the inherited characteristics of a population over successive generations. An individual may change during its lifetime because of growth, learning, exercise, or environmental effects, but such acquired changes generally do not alter the population’s hereditary makeup. Evolution requires heritable variation, reproduction, and changes in trait frequencies over time. Therefore option A is correct; the other choices confuse individual development with population evolution.

Fossils are preserved remains or traces that provide a record of organisms living in the past and can show changes through geological time. Homologous organs have the same basic structural plan in different organisms, even when their functions differ, suggesting inheritance from a common ancestor followed by modification. Together, these forms of evidence support evolutionary relationships. Thus option A is correct; the other choices are unrelated to fossils or comparative anatomy.

Inheritance allows a variation to pass from parents to offspring. If a small change improves survival or reproductive success, natural selection may make it more common in later generations. Other variations can accumulate with it, and the combined shift in trait frequencies can gradually produce a major difference in the population. Therefore option A is correct. The distractors contradict inheritance or incorrectly treat evolutionary change as immediate or unrelated to populations.

Natural selection is context-dependent: a trait that is advantageous in one environment may provide little benefit or even become disadvantageous when conditions change. For example, a change in climate, food availability, or predators can alter which variations improve survival and reproduction. Consequently, the direction of selection may shift toward different traits. Option A is correct; identical organisms provide no variation for selection, and without reproduction or chromosomes the proposed process cannot operate normally.

Heredity explains how genetic information and traits pass from parents to offspring, while evolution describes changes in inherited characteristics in populations over many generations. Heritable variation is essential because natural selection, genetic drift, and other processes can act on it. Thus, the two topics are scientifically connected. Option A is correct; the other choices deny their biological relationship or confuse them with unrelated processes.

A scar is an acquired characteristic produced by injury during an individual’s lifetime. It generally affects somatic, or body, cells and does not alter the DNA of the germ cells that form eggs or sperm. Since hereditary information is transmitted through germ cells, the scar is not normally inherited by offspring. Therefore option A is correct; dominance, absence of chromosomes, and fossilisation are unrelated explanations.